1. Filed of the Invention
The invention relates to an interchangeable holder for hollow drills, containing a carrier part for end accommodation of the base end of the drill rod of the hollow drill, and a holding means for retaining engagement of the carrier part on the assigned recesses which are made in the wall of the drill rod on its base end.
The invention also relates to a hollow drill for fixing on an interchangeable holder, the drill rod of the hollow drill having, on the base end opposite the drill tip, recesses for producing bayonet-like retaining engagement to a holding means of the interchangeable holder and each recess having an entry section for the holding means.
2. Description of Related Art
Published German Patent Application DE 198 18 284 A1 discloses a core cutting tool for masonry with a interchangeable holder which has a carrier disk with a central hollow journal which can be fixed on the hollow shaft which can be clamped in a drill chuck for driving the carrier disk. The carrier disk contains on its end face, which is opposite the journal, which is perpendicular to the axis of rotation, and which forms a contact surface for a hollow rod of the core cutting tool, an outer annular wall which is located on the periphery of the carrier disk, a middle annular wall which is located at a short distance from the outer wall, and an inner annular wall. Three holding pins run radially from the inner wall through the middle wall to the outer wall, their being located spaced apart from the end face and offset by 120° each against one another. The hollow rod contains, on its base end opposite the cutting teeth, three L-shaped slots which are located offset by 120° on the periphery of the hollow rod and with the holding pins of the hollow rod which adjoins the end face of the carrier disk form a quarter-turn fastener. Here, the inside of the hollow rod directly borders the outside of the middle annular wall and the brackets formed by the L-shaped slots press elastically against the outside of the middle annular wall so that the hollow rod is held centrally on the carrier disk. On the bracket a projection can be formed which can fit into the assigned recess in the outside of the middle annular wall and thus can form an interlock of the hollow rod on the carrier disk. This core cutting tool is designed to hold a hollow rod of a certain diameter which directly extends over the middle annular wall. There is no accommodation of hollow rods with diameters which differ arbitrarily within a range and due to the type of interlocking of the brackets which require direct contact against the outside of the middle annular wall, there can be no accommodation.